Energetics of burrowing, running, and free‐living in the Namib Desert golden mole (Eremitalpa namibensis)

Abstract

The Namib Desert golden mole (Eremitalpa granti namibensis) is a small (c. 20 g), blind, sand-swimming, chrysochlorid insectivore that inhabits the sand dunes of one of the driest and least productive areas of the world. Its food, largely termites, is sparse and occurs in widely distributed patches, and free water is unavailable. The moles forage by running on the surface and burrowing below the sand. We estimated their daily energy expenditure in the ®eld to be 11.8 kJ d -1 by constructing a`distance-energy budget' based on measurements of tracks in the sand and the energy cost of running (4.2 kJ d -1 ), burrowing (3.2 kJ d -1 ), and resting (4.4 kJ d -1 ). We also measured ®eld metabolic rate (12.5 kJ d -1 ) and water turnover (2.3 ml d -1 ) independently with doubly-labelled water. The resting metabolic rate (0.5 ml O 2 g -1 h -1 at 35 8C) is about a ®fth of that predicted for a normal insectivorous mammal, and the daily ®eld energy expenditure and water turnover are about a half. The low daily energy expenditure stems mainly from the low resting metabolic rate, which is associated with low body temperatures and metabolic depression. Moles save more energy during foraging by running on the surface of the sand, rather than burrowing under it. The gross energy cost of sand-swimming (80 J m -1 ) is 26 times more expensive than running on the surface (3.0 J m -1 ), but is less than a tenth of the energy required by mammals that tunnel through compact soil. Nevertheless, it would be energetically impossible for the moles to obtain enough food by foraging only underground at our study site. The mean track length was 1.4 km, but only 16 m of it was below the surface. There is evidence that the track length and fraction underground depend on food abundance which is in¯uenced by rainfall.

Digestive Tract Morphology and Gut Microbiota Jointly Determine an Efficient Digestive Strategy in Subterranean Rodents: Plateau Zokor

“…The unique underground lifestyle of the subterranean rodents determines high energy expenditure in their life history such as digging format, foraging and other activities [ 25 , 26 ]. For foraging, the energy consumption is enormous, so they need to have a more efficient diet digestibility to buffer the energy expenditure [ 27 , 28 ]. Plateau zokor, a typical subterranean rodent, is accompanied by excavation activities and consumes more energy compared with ground rodents [ 27 , 28 ].…”

“…Plateau zokor ( Eospalax baileyi ) is a solitary and entirely subterranean burrowing endemic rodent species, inhabiting areas of 2600 to 4600 m above sea level on Qinghai-Tibet Plateau [ 23 , 24 ]. Plateau zokor spend most their life in underground nests and foraging, and burrowing activity mainly takes place at a depth of 3–20 cm under the ground [ 28 ]. This underground lifestyle means that plateau zokor must excavate for courtship and foraging [ 25 , 26 ].…”

Do endotherms have thermal performance curves?

“…Bergh and Ekblom, 1979;Sawka et al, 2012) are rare, largely because of the difficulties in manipulating T b in a standardisable way. A handful of studies, mostly in small mammals, have been able to measure wholebody performance (in the form of righting time, running speed or the ability to pull a weight) at higher T b with mixed results, with some showing an increase in performance at higher T b (Seymour et al, 1998;Rojas et al, 2012;Stawski et al, 2017;Treat et al, 2018), whereas others found no difference (Wooden and Walsberg, 2004). Studies that directly measure muscle performance in relation to muscle temperature in endotherms (with the exception of studies on humans) are equally rare and have found differences according to which muscle (core versus periphery) is measured, the temperatures under which the muscles developed, as well as the species (Angilletta et al, 2010;James et al, 2015;Little and Seebacher, 2016;Rummel et al, 2018).…”

Flight metabolic rate of Locusta migratoria in relation to oxygen partial pressure in atmospheres of varying diffusivity and density

“…The raw recordings of CO 2 production were instantaneously corrected by applying an empirically derived washout constant for the chamber using previously described principles (Seymour et al, 1998). Instantaneous CO 2 production rates (µmol s −1 ) were calculated as the product of incurrent flow rate and the fraction of CO 2 added to the excurrent air (Lighton, 2008), and then converted to instantaneous metabolic rate (mW) assuming a respiratory exchange ratio of 0.86, as determined in pilot experiments, and a conversion factor of 0.54 J µmol −1 (Withers, 1992).…”